Japanese patent publication No. 55-19366 discloses an automatic door operating system in which the distance of travel of the door from its rest position is determined by counting pulses generated so as to be proportional to the number of rotations of the driving motor, and the door is controlled by comparing the pulse count with a pre-set value corresponding to the total length of travel of the door.
Such an arrangement represents a significant advance over earlier prior art systems where devices such as limit switches were employed to define the door travel, but does not provide for a self-commissioning operation, in particular requiring the total door travel to be pre-set.